Various anti-fogging agents are widely used in order to prevent fogging in silver halide photosensitive materials. As anti-fogging agents, heterocyclic compounds are preferably used as described, for example, in "Fundamentals of Photographic Technology--Silver Salt Photography--, pages 194-198 (The Photographic Society of Japan, 1979)". As the most effective heterocyclic compound, similar compounds containing a mercapto group are available. By adding such compounds which work as an anti-fogging agent to a photosensitive material, the fogging caused during storage or developing process of the photosensitive material may be satisfactorily minimized.
Yet, even if such an effective anti-fogging agent is added into a silver halide emulsion, the sensitivity of the emulsion often decreases. Consequently, the more effectively the fogging is suppressed, the more seriously and disadvantageously the sensitivity decreases.
Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No.36130/1976 disclosed a proposal, which was intended to solve such a sensitivity-fogging dilemma, whereby a silver halide emulsion essentially consisting of cubic crystals and silver halide content thereof containing more than 80 mol % silver chloride or silver bromide is sensitized with sulfer wherein a mercapto compound, having a pKa value not exceeding 7.6 and containing at least two nitrogen atoms, is added into the emulsion.
Yet, such requirements greatly limit the scope of composition of a silver halide emulsion, limiting the field of application of a photosensitive material based on such a prior art. Additionally, the experimental results learned by the inventor of the present invention, and other persons, revealed that the effect of the above-mentioned mercapto compound is lost, because of standing, before a silver halide emulsion, in which a like compound is added after chemically ripening the emulsion, is coated on a support, decreasing sensitivity, and that when the emulsion is cooled to set after the mercapto compound is added, the sensitivity also decreases, and that the scope of conditions where the silver halide photosensitive material is employed are strictly limited.
Additionally, in the case of certain effective mercapto compounds, even if an effective mercapto compound is added into a coating solution ready for coating prepared by cooling and setting a chemically ripened silver halide emulsion and by warming and melting it, in order to prevent the deterioration of sensitivity during the cooling and setting of such a silver halide emulsion, a like emulsion loses sensitivity when it is allowed to stand, thus limiting the scope of its application.
On the other hand, Japanese Patent O.P.I. Publication No. 164734/1982, No. 79436/1980 and No. 18327/1974, for example, disclosed that a mercapto compound may be added into a nonphotosensitive layer which does not contain a silver halide emulsion. However, with every example disclosed by the specifications mentioned above, a mercapto compound is added only into a silver halide emulsion layer, and, additionally, some of the specifications state that a similar compound should be preferably contained in the silver halide emulsion layer.
Further, Japanese Patent O.P.I. Publication No. 102621/1973 disclosed that a specific mercapto compound may be added to an arbitrarily designated photographic structural layer. However, though the specification disclosed examples where a specific mercapto compound is respectively added into a protective layer and a silver halide emulsion layer, and, of which effect is centered upon, like the examples mentioned before, the anti-fogging effect as well as anti-desensitization effect, the specification totally failed to state the features and benefits for a case where a mercapto compound is added into a non-photosensitive layer, or, the merits for the case where a mercapto compound is added into a plurality of nonphotosensitive layers of a silver halide photosensitive material.
Incidentally, if a photosensitive material is, as seen with a multi-layered color photographic material, composed on a plurality of silver halide emulsion layers, the antifogging and desensitization effects of a mercapto compound added to specific emulsion layers often cause the desensitization and anti-fogging effects not only in layers where the mercapto compound is added, but in other silver halide emulsion layers.